This weekend, activists will attempt to block the unloading of a container ship in Oakland, California. Here's what's going on, and what's behind it.

What is Block The Boat?Block the Boat is a political campaign of nonviolent direct action against the state of Israel that bills itself as similar to the anti-apartheid movement against white South Africa — one of the first major boycotts of which also happened at the Oakland port back in 1984. By throwing sand in the gears of the Israeli economy, Block the Boat seek to change Israeli policy towards Gaza and the West Bank.

Which company is being targeted?Zim Shipping, the largest shipper in Israel and the 10th-largest shipping company worldwide. The company was outright controlled by the Israeli government for many years, and though it was privatized in 2004, the Israeli state still owns a large "golden share" in the company and regards it as a national security asset. The golden share allows Israel certain rights over the company, such as a veto power over the transfer of 35 percent or more of Zim shares, and the ability to draft Zim ships into military service.

What is the objective?This weekend, protesters will attempt to block the unloading of a Zim container ship in Oakland. Through the use of public tracking data and investigative work, they have determined which berth the ship will be using, and set up a picket line there — though workers who so wish will be allowed through. According to movement organizers, they have a good relationship with the local branch of the International Longshore and Warehouse Union, so they think few workers will break the picket, at least at first. (Sympathy strikes are illegal under the Taft-Hartley Act, so the union leadership can't do anything official.)

What do the protesters want?Broadly speaking, justice for Palestinians. Since 1967, Israel has occupied Palestinian lands in the West Bank and Gaza. In line with the Boycott, Divestment, and Sanctions movement, they want an end to occupation, the restoration of human rights to all Arabs and Palestinians under Israeli control, and the right of return.

They also have more specific demands with respect to Gaza, which has been under a crushing blockade for many years. (A Turkish flotilla that tried to run the blockade back in 2010 was sacked by Israeli commandos, who killed nine people in the process, including an American citizen.) The protesters demand free movement in and out of Gaza, free use of the Gaza seaport, and unrestricted trade in goods.

Will this work?In fact, it's already working to some degree. The boat was scheduled to unload Saturday, but recently rescheduled to Sunday in an attempt to avoid the picket. The protest has been correspondingly moved. A previous effort in August also worked fairly well, holding up a different Zim ship for four days. According to movement organizers, their intelligence work on that occasion was good enough to allow them to anticipate an attempt at misdirection by steaming out and back into the harbor.

Of course, Israel has almost unanimous support among both parties in the U.S., so this almost certainly won't change Israeli policy all by itself. But as part of a long campaign it could be a fairly powerful tool, as the eventual end of apartheid in South Africa shows. Modern container ships are very large and their movements are scheduled months in advance. Screwing up their timetable has to be very expensive.